With the rapid growth of private cars, roads are more and more crowded, so that traffic accidents happen frequently, and therefore, the safety performance of automobiles becomes important. When a collision accident happens to a vehicle, the automobile safety air bag can alleviate the injury degree of the personnel, and the passenger and the driver are prevented from colliding a second time, or being thrown away from the seats under dangerous situations such as rolling of the vehicle. Usually, automobile air bags are arranged in the front of an automobile (in front of the driver's seat and the passenger's seat). However, in order to protect the driver's life safety, the air bags can be installed at not only the driver's seat and the passenger's seat, but also the sides of the automobile (in the front and back portions of the automobile) and the roof thereof, so that the air bags or the air curtains are installed in the three sides of the vehicle. As a result, the number of steel pipes for the air bags on each automobile is increased. In order to improve the safety performance of the automobile, the quality of the steel pipe for the air bag on the automobile can also be improved, and the steel tube is required to have high strength-toughness product and thin wall thickness, such that the requirements of safety, light weight and low cost for the vehicle can be met.
The mechanism of the automobile air bag is as follows: when a gas generator equipped with a burst agent senses a speed change caused by a collision, an ignition action is triggered according to a signal indication, such that the solid fuel is ignited, and a gas is generated to inflate the air bag, then the air bag is rapidly expanded. Thus, the impact on the human body during collision is reduced. During the manufacture of a gas generator of an air bag, the seamless steel tube is generally required to have high bursting strength, high strength-toughness product and low-temperature impact toughness.
JP2002-294339, published on Oct. 9, 2002 and entitled “A steel for air bag having excellent weldability, excellent molding, high dimensional precision, high tensile strength, and excellent burst resistance, and a method for producing same”, relates to a steel for air bags and a manufacturing method thereof. The steel material comprises the following components (wt. %): C: 0.05-0.20%; Si: 0.1-1.0%; Mn: 0.20%-2.0%; P<0.025%; S<0.010%; Cr: 0.05-1.0%; Al<0.10%, Mo<0.50%; Ni<1.5%; Cu<0.5%, V<0.2%; Ti<0.1%, Nb<0.1%; B<0.005% and the balance of Fe and inevitable impurities. In the manufacturing method in the Japanese patent document, the steel tube is heated and then quenched to the temperature of the Ac1 phase transition point (at least), and then the steel tube is annealed at the temperature of the Ac1 phase transition point.
CN102304613A, published on Jan. 4, 2012 and entitled “Steel tube for air bag system and method for producing same”, discloses a seamless steel tube for an air hag and a manufacturing method thereof. The steel tube comprises the following components, by wt %: C: ≤9.12%, Mn: 1.00-1.40%, S: ≤01%, P: ≤0.015%, Si: 0.15-0.35%, Ni: ≤0.25%, Cr: 0.40-0.80%, Mo: 0.30-0.60%, V: ≥0.07%, Cu: ≤0.35%, Al: 0.15-0.05%, Ne: ≤0.05%, Ti: ≤0.05%, Sn: ≤0.05%, Sb: ≤0.05%, As: ≤0.05%, Pb: ≤0.05%, and the sum of the amounts of Sn, Sb, As and Pb is ≤0.15%, and the balance of Fe. The Chinese patent document also discloses a manufacturing method of the seamless steel tube.
The manufacturing methods of the steel or the seamless steel tube disclosed by the above two patent documents need the heat treatment of quenching and tempering to the corresponding steel or the seamless steel tube in order to achieve higher tensile strength.
CN101528964A, published on Sep. 9, 2009 and entitled “Seamless steel tube for accumulator in air bag and a method for producing same”, relates to a seamless steel tube and a manufacturing method thereof. The seamless steel tube comprises the following component, by wt %: C: 0.08-0.20%, Si: 0.1-1.0%, Mn: 0.6-2.0%, P: ≤0.025%, S: ≤0.010%, Cr: 0.05-1.0%, Mo: 0.05-1.0%, Al: 0.002-0.10%, at least one selected from the group consisting of Ca: 0.0003-0.01%, Mg: 0.0003-0.01%, and REM (rare earth elements): 0.0003-0.01%, and at least one selected from the group consisting of Ti: 0.002-0.1% and Nb: 0.002-0.1%, CEQ defined by the following equation (1) falling into the range of 0.45˜0.63,CEQ=C+Si/24+Mn/6+(Cr+Mo)/5+(Ni+Cu)/15  (1).
The above Chinese patent document used a heat treatment of normalizing and tempering to achieve high strength and high toughness. However, the above seamless steel tube contained Ca, Mg and rare earth elements, so that the manufacturing cost of the steel tube is increased.